Photoresist and other resist material such as electron beam or ion beam resist is used in semiconductor processing to fabricate masks that allow etching of selected portions of a chip at any level. Resist materials are usually organic polymers that change state in response to irradiation of small portions of the resist material by a beam of photons (visible, ultraviolet, X-ray) or charged particles such as electrons or ions. In a positive resist material, irradiation produces local decomposition of the resist constituents into lower molecular weight polymers so that the etchant attacks these areas more readily than it attacks constituents in the unirradiated areas. In a negative resist material, irradiation produces cross-linking among the polymers so that the resulting higher molecular weight constituents resist etching action more successfully than do constituents in the unirradiated areas. This cross-linking produces a swelling of negative resist material so that optical resolution in a negative resist is usually limited to 1.5 .mu.m or more. However, positive and negative resist materials are initially fabricated in a similar manner. The substrate is often oxidized or unoxidized Si or GaAs, doped or undoped.